Sets the step-limit used by the ACL2 prover
This event provides a way to limit the number of so-called ``prover
steps'' permitted for an event. See with-prover-step-limit for a way
to specify the limit on prover steps for a single event, rather than globally.
For a related utility based on time instead of prover steps, see with-prover-time-limit. For examples of how step limits work, see the
Note: This is an event! It does not print the usual event summary but nevertheless changes the ACL2 logical world and is so recorded. Moreover, its effect is to set the ACL2-defaults-table, and hence its effect is local to the book or encapsulate form containing it; see ACL2-defaults-table.
Example Forms: (set-prover-step-limit *default-step-limit*) ; no limit on prover steps (set-prover-step-limit nil) ; abbreviation for the form just above (set-prover-step-limit 10000) ; allow at most 10,000 prover steps per event General Form: (set-prover-step-limit expr)
This event specifies the limit on the number of ``steps'' counted by the
ACL2 prover during processing of an event. Currently, a step is counted for
each call of the system functions
Depending on the computer you are using, you may have less than a half-hour
of time before the number of prover steps exceeds the maximum step-limit,
which is one less than the value of
There is at best a loose connection between the counting of steps and
with-prover-time-limit. In particular, for a call of
The limit is relevant for every event, as well as for calls of thm
and certify-book — and more generally, to any form that creates
a ``summary context'' to print the usual event summary. The limit is
also put in force when entering the interactive proof-builder. A call
The limit applies to each event, not just ``atomic'' events. Consider the following example.
(set-prover-step-limit 500) (encapsulate () (defthm lemma-1 ; takes 380 steps (equal (append (append x y) z) (append x y z)) :rule-classes nil) (defthm lemma-2 ; would take 319 steps (equal (len (append x y)) (+ (len x) (len y))) :rule-classes nil))
Prover steps counted: 380 LEMMA-1
The second defthm event,
ACL2 Error in STEP-LIMIT: The prover step-limit, which is 120 in the current context, has been exceeded. See :DOC set-prover-step-limit.
The summary for
Prover steps counted: More than 120
The summary for the encapsulate event then indicates that the available steps for that event have also been exceeded:
Prover steps counted: More than 500
The discussion above applies to any event that contains other events, hence applies similarly to progn events.
For those who use make-event, we note that prover steps in the
expansion phase similarly contribute to the total number of steps counted.
For example, suppose that the limit is 500 prover steps as above, and you
ACL2 !>(make-event (er-progn (mini-proveall) (value '(value-triple nil)))) [[... output omitted here ...]] Summary Form: ( MAKE-EVENT (ER-PROGN ...)) Rules: NIL Warnings: Double-rewrite, Equiv, Subsume and Non-rec Time: 0.38 seconds (prove: 0.04, print: 0.29, other: 0.05) Prover steps counted: 41090 NIL ACL2 !>